They are evergreenshrubs and small trees growing to 1–15 metres (3.3–49.2 ft) tall. The leaves are opposite or in whorls of three or four, 5–50 centimetres (2.0–19.7 in) long and 3–25 centimetres (1.2–9.8 in) broad, dark green and glossy with a leathery texture. The flowers are solitary or in small clusters, white, or pale yellow, with a tubular-based corolla with 5-12 lobes (petals) from 5–12 centimetres (2.0–4.7 in) diameter. Flowering is from about mid-spring to mid-summer, and many species are strongly scented.

Gardenia plants are prized for the strong sweet scent of their flowers, which can be very large in size in some species.

Gardenia jasminoides (syn. G. grandiflora, G. Florida) is cultivated as a house plant. This species can be difficult to grow because it originated in warm humid tropical areas. It demands high humidity to thrive, and bright (not direct) light. It flourishes in acidic soils with good drainage and thrives on [68-74 F temperatures (20-23 C)][4] during the day and 60 F (15-16 C) in the evening. Potting soils developed especially for gardenias are available. G. jasminoides grows no larger than 18 inches in height and width when grown indoors. In climates where it can be grown outdoors, it can attain a height of 6 feet. If water touches the flowers, they will turn brown.[5]

In China and Japan, Gardenia jasminoides is called zhīzi (栀子) and kuchinashi (梔), respectively. Its fruit is used as a yellow dye,[6] used on fabric and food (including the Korean mung bean jelly called hwangpomuk). Its fruits are also used in traditional Chinese medicine for their clearing, calming, and cooling properties.[7]